A mysterious gaseous smell has been reported across large portions of New York City, prompting the city’s Hazardous Materials teams (HAZMAT), police department and fire department to be deployed.

Four Manhattan school have been evacuated so far, according to the Associated Press, while some subway and automobile traffic has been stopped in the areas affected.

There is no word yet as to the source of the strange gas, which prompted hundreds of calls to police and fire officials.

The New York City Fire Department reported that it began receiving calls about the odor around 9 a.m. Eastern time. Since then, it has spread from Midtown Manhattan at the island’s center, to Battery Park City in southern Manhattan, and across the Hudson River to the west in Weehawken and Jersey City, N.J.

A large number of New Yorkers are still concerned about potential terror threats to their city following the attacks on New York in September 11, 2001, which killed more than 2,700 people.